Currently, region-specific information is disseminated by predetermined point-to-point communication or by general broadcast which must be manually monitored in order to extract information peculiar to a position, velocity and time of interest. For example, marine weather data is continuously broadcast. However, mariners must monitor the broadcast for long periods of time in order to obtain the information peculiar to their region. Even then, the exact region affected may require computation or may be ambiguously defined. There is also the possibility that the user may miss information of interest because he or she occupies an unknown location, is unfamiliar with the region, or uses a different frame of reference, among other reasons.
Another example is tactical ballistic missile (TBM) warning, which is derived from space and ground based sensor data, and is provided through a variety of broadcast and general purpose communications systems to a small subset of in-theater forces. Currently, such warning requires transportable processing stations that can generate information about specific situations in the field but cannot directly communicate with all individuals affected. The timeliness, reliability, and dispersion of information under these conditions are of concern. Because warning is in the form of geographical coordinates and time of predicted impact, users must interpret the data to determine if the warning affects them.
Some current commercial systems are using Global Positioning System information to select relevant data from computer based files such as appropriate electronically stored maps for use in automobiles. These are useful for relatively static information but fail to address dynamic environmental or combat factors.
U.S. Pat. No. 5,243,652 to Teare et al. discloses a database access system in which each mobile user has a positioning system which transmits position information to a central facility. This central facility then grants or denies database access depending on the geographical location of the mobile user.
U.S. Pat. No. 4,860,352 to Laurance et al. discloses a system in which a satellite system determines the position of a transmitter at a first location and a receiver at a second location. The transmitter position is appended to the received message which is sent by the satellite system to the receiver. The receiver receives the appended message, extracts the transmitter position data and compares the extracted transmitter position with a stored transmitter position. If the positions correlate, the receiver knows it has received an authentic message.
None of these devices allow for automated receiver discrimination of any message broadcast generally in order to only disseminate relevant messages.